We use this expression to say we don’t know something and need to check to find out.
You can use this phrase in ………… language.
Spoken
Written
Informal
Example 1
A: Where’s the document?
B: I don’t know offhand. Have you checked his desk?
Example 2
A: Is Ostrava closer to Prague than Olomouc?
B: I don’t know offhand. I have to google it.